In the sewing sections of stores there are very fine monofilament sewing threads that seem to be about 5X, or finer. I know these have been used a lot in fly tying but have they been used as tippets? They are labelled as nylon but should I be concerned about quality in terms of weak spots etc. Please comment. 
Ray,
Like others, I use them in tying and I have found them to be âinconsistentâ at best in the strength. I know I wouldnât use them for tippet material. Some things are worth spending the few extra bucks on and good tippet material is one of them in my opinion. Just my two cents worth.
Jim Smith
Most of the sewing mono that Iâve seen sold measures in at around .004 - .005. Actual, itâs been used for years as a secret tool for ice fisherman who want to fish ultra-light for panfish. Most of the thread usually tests out about 1 lb, give or take a bit. It also has a high degree of stretch. The high degree of stretch, coupled with an ultra light ice fishing rod allows it to function well when ice fishing. But in the ice fishing application, there is a long section of line being used, so it provides alot of stretch. If it was used as a tippet, the margin of error (stretch) would be much less.
Itâs also not particularly easy to use when it comes to knots.
I have furled a few leaders out of it and it seems to work ok on my 4wt with small flies. never used it as tippet thoughâŚ
My wife tells me that its sometimes called invisible thread. She also says that it stretches pretty easy, and sheâs stopped using it for sewing because she doesnât want it to break (a single strand breaks fairly easily) and get tangled up inside her machine. Iâd stick with plain old fishing mono. I like Berkleyâs XL (extra limp). But then again, Iâm pretty cheap.
JoeâŚwouldnât the word be âfrugalâ:D;)
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per The Thread Exchange ( [FONT=Tunga]http://www.thethreadexchange.com/miva/merchant.mvc?Screen=CTGY&Store_Code=TTE&Category_Code=monofilament-information ) :
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Monofilament Thread Information[/b]
[b]Monofilament thread looks like fishing line but it is a terrible fishing line alternative. It is the wrong color, too stretchy, and to prone to tangling on reels. Donât even think about trying to catch fish with this thread and donât even think of sewing with fishing line.
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like others, iâve made furled leaders from it and that works ok, but never used it for tippet. itâs sort of kinky coming off the spool. i find its breaking strength inconsistent, especially at knotting. lets face it. it wasnât designed for angling applications and as a sewing application i think it sort of sucks. it just doesnât hold up very well and no telling how long its been sitting on the shop shelf. good mono tippet material isnât that expensive anyway.